The present invention relates to a method of manufacturing a semiconductor device and to a semiconductor device manufactured by the method. More particularly, the present invention relates to a method of manufacturing a semiconductor device including a plurality of Metal Oxide Semiconductor field effect transistors (MOSFETs) having different operating voltages. The invention also pertains to a semiconductor device manufactured by the method.
In recent LSIs, a MOSFET (HV-Tr) operating at relatively high voltages such as 3.3 V and 2.5 V like I/O transistors and a MOSFET (LV-Tr) operating at relatively low voltages such as 1.2 V like high performance logic transistors are often mounted mixedly on the same substrate.
When the HV-Tr and LV-Tr having different operating voltages are thus mixedly mounted on the same substrate, the following steps must be performed. That is, sizes of constituent elements, for example gate insulating film or gate electrode, of the respective transistors are optimized. Alternatively, impurities (dopants) are doped, under conditions suitable for the respective transistors, by ion implantation into channel forming regions of the transistors to adjust threshold voltages (Vths). Further, there has been conventionally proposed a method of forming a punch-through stopper structure suitable for each transistor to prevent the so-called punch-through phenomenon.
When complementary HV-Trs and LV-Trs are mixedly mounted, ion implantations for Vth adjustment are performed into channel forming regions of the respective n-channel and p-channel HV-Trs and into channel forming regions of the respective n-channel and p-channel LV-Trs, respectively. More specifically, at least four types (sheets) of reticles are required for the ion implantation for Vth adjustment.
Before performing the ion implantations for Vth adjustment, there are usually performed ion implantations for forming p-well regions both of the n-channel HV-Tr and LV-Tr, and n-well regions both of the p-channel HV-Tr and LV-Tr, respectively. When those ion implantations are added, at least a total of six reticles are required by the time the ion implantations for Vth adjustment are completed.
When the number of used reticles thus increases, the number of processes increases and the LSI production cost including the reticle fabrication cost disadvantageously increases.